How to enumerate IP addresses of all enabled NIC cards from Java?

Asked 30/1, 2009 at 4:13 Answered 26/3, 2013 at 15:28

Short of parsing the output of ipconfig, does anyone have a 100% pure java way of doing this?

Galore answered 30/1, 2009 at 4:13 Comment(0)

This is pretty easy:

try {
  InetAddress localhost = InetAddress.getLocalHost();
  LOG.info(" IP Addr: " + localhost.getHostAddress());
  // Just in case this host has multiple IP addresses....
  InetAddress[] allMyIps = InetAddress.getAllByName(localhost.getCanonicalHostName());
  if (allMyIps != null && allMyIps.length > 1) {
    LOG.info(" Full list of IP addresses:");
    for (int i = 0; i < allMyIps.length; i++) {
      LOG.info("    " + allMyIps[i]);
    }
  }
} catch (UnknownHostException e) {
  LOG.info(" (error retrieving server host name)");
}

try {
  LOG.info("Full list of Network Interfaces:");
  for (Enumeration<NetworkInterface> en = NetworkInterface.getNetworkInterfaces(); en.hasMoreElements();) {
    NetworkInterface intf = en.nextElement();
    LOG.info("    " + intf.getName() + " " + intf.getDisplayName());
    for (Enumeration<InetAddress> enumIpAddr = intf.getInetAddresses(); enumIpAddr.hasMoreElements(); ) {
      LOG.info("        " + enumIpAddr.nextElement().toString());
    }
  }
} catch (SocketException e) {
  LOG.info(" (error retrieving network interface list)");
}

Limelight answered 30/1, 2009 at 4:18 Comment(2)

Thanks for the example. There is a bug in it though(and in all other examples here), getNetworkInterfaces() can return null for some strange reason(please tell me why) if no network interfaces are found: 'Returns all the interfaces on this machine. Returns null if no network interfaces could be found on this machine. NOTE: can use getNetworkInterfaces()+getInetAddresses() to obtain all IP addresses for this node ' – Reviewer 21/9, 2009 at 8:17

Version with LOG.infos replaced with System out calls and imports included here: gist.github.com/williamberg/5299998 – Derayne 3/4, 2013 at 10:17

Some of this will only work in JDK 1.6 and above (one of the methods was added in that release.)

List<InetAddress> addrList = new ArrayList<InetAddress>();
for(Enumeration<NetworkInterface> eni = NetworkInterface.getNetworkInterfaces(); eni.hasMoreElements(); ) {
   final NetworkInterface ifc = eni.nextElement();
   if(ifc.isUp()) {
      for(Enumeration<InetAddress> ena = ifc.getInetAddresses(); ena.hasMoreElements(); ) {
        addrList.add(ena.nextElement());
      }
   }
}

Prior to 1.6, it's a bit more difficult - isUp() isn't supported until then.

FWIW: The Javadocs note that this is the correct approach for getting all of the IP addresses for a node:

NOTE: can use getNetworkInterfaces()+getInetAddresses() to obtain all IP addresses for this node

Osithe answered 30/1, 2009 at 4:38 Comment(9)

According to the JavaDoc, NetworkInterface and its methods were added in 1.4. I've personally been using code similar to what I posted since Java 5, so I haven't tested my code with Java 1.4 or earlier. – Limelight 30/1, 2009 at 4:55

Actually, please edit your post to remove the erroneous comment "Prior to 1.6, there is no way to do this 100% pure java....parsing Runtime results or JNI would be your only options." as only the ifUp() method you used was added in 1.6. The rest is present since 1.4. – Limelight 30/1, 2009 at 4:59

The NetworkInterface class is present since 1.4, but the getInterfaceAddresses() and isUp() methods are both @since 1.6 (according to java.sun.com/javase/6/docs/api/java/net/NetworkInterface.html). 1.6 made the NetworkInterface class MUCH richer than it was in 1.5. – Osithe 30/1, 2009 at 5:17

errr, I see what you're saying.... getInetAddresses() is @since 1.4 (at least)... Editted to reflect some doubt while I figure things out :). – Osithe 30/1, 2009 at 5:20

But you are using only ifUp(). Your sample does not use getInterfaceAddresses(). Don't scare people off of using this code with Java 5 or Java 1.4! Yes, the Java 6 update added quite a lot to NetworkInterface. – Limelight 30/1, 2009 at 5:22

Our comment electrons flew past each other in cyberspace :P – Osithe 30/1, 2009 at 5:29

I believe the other thing your code uses that is new to 1.6 is using an Enumeration with the Java 5 for/each loop. Sure makes it look cleaner! – Limelight 30/1, 2009 at 14:37

This doesn't compile in JDK 1.7. getNetworkInterfaces returns an Enumeration which does not implement Iterable. – Stylet 11/7, 2012 at 19:58

On JDK 1.7 turn the Enumeration into something iterable with Collections.list() – Alight 21/5, 2014 at 20:50

This code only works in Java 1.6 because of the added InterfaceAddress code.

  try
  {
     System.out.println("Output of Network Interrogation:");
     System.out.println("********************************\n");

     InetAddress theLocalhost = InetAddress.getLocalHost();
     System.out.println(" LOCALHOST INFO");
     if(theLocalhost != null)
     {
        System.out.println("          host: " + theLocalhost.getHostName());
        System.out.println("         class: " + theLocalhost.getClass().getSimpleName());
        System.out.println("            ip: " + theLocalhost.getHostAddress());
        System.out.println("         chost: " + theLocalhost.getCanonicalHostName());
        System.out.println("      byteaddr: " + toMACAddrString(theLocalhost.getAddress()));
        System.out.println("    sitelocal?: " + theLocalhost.isSiteLocalAddress());
        System.out.println("");
     }
     else
     {
        System.out.println(" localhost was null");
     }

     Enumeration<NetworkInterface> theIntfList = NetworkInterface.getNetworkInterfaces();
     List<InterfaceAddress> theAddrList = null;
     NetworkInterface theIntf = null;
     InetAddress theAddr = null;

     while(theIntfList.hasMoreElements())
     {
        theIntf = theIntfList.nextElement();

        System.out.println("--------------------");
        System.out.println(" " + theIntf.getDisplayName());
        System.out.println("          name: " + theIntf.getName());
        System.out.println("           mac: " + toMACAddrString(theIntf.getHardwareAddress()));
        System.out.println("           mtu: " + theIntf.getMTU());
        System.out.println("        mcast?: " + theIntf.supportsMulticast());
        System.out.println("     loopback?: " + theIntf.isLoopback());
        System.out.println("          ptp?: " + theIntf.isPointToPoint());
        System.out.println("      virtual?: " + theIntf.isVirtual());
        System.out.println("           up?: " + theIntf.isUp());

        theAddrList = theIntf.getInterfaceAddresses();
        System.out.println("     int addrs: " + theAddrList.size() + " total.");
        int addrindex = 0;
        for(InterfaceAddress intAddr : theAddrList)
        {
           addrindex++;
           theAddr = intAddr.getAddress();
           System.out.println("            " + addrindex + ").");
           System.out.println("            host: " + theAddr.getHostName());
           System.out.println("           class: " + theAddr.getClass().getSimpleName());
           System.out.println("              ip: " + theAddr.getHostAddress() + "/" + intAddr.getNetworkPrefixLength());
           System.out.println("           bcast: " + intAddr.getBroadcast().getHostAddress());
           int maskInt = Integer.MIN_VALUE >> (intAddr.getNetworkPrefixLength()-1);
           System.out.println("            mask: " + toIPAddrString(maskInt));
           System.out.println("           chost: " + theAddr.getCanonicalHostName());
           System.out.println("        byteaddr: " + toMACAddrString(theAddr.getAddress()));
           System.out.println("      sitelocal?: " + theAddr.isSiteLocalAddress());
           System.out.println("");
        }
     }
  }
  catch (SocketException e)
  {
     e.printStackTrace();
  }
  catch (UnknownHostException e)
  {
     e.printStackTrace();
  }

The "toMACAddrString" method looks like this:

public static String toMACAddrString(byte[] a)
{
  if (a == null)
  {
     return "null";
  }
  int iMax = a.length - 1;

  if (iMax == -1)
  {
     return "[]";
  }

  StringBuilder b = new StringBuilder();
  b.append('[');
  for (int i = 0;; i++)
  {
     b.append(String.format("%1$02x", a[i]));

     if (i == iMax)
     {
        return b.append(']').toString();
     }
     b.append(":");
  }
}

and the "toIPAddrString" method is here:

public static String toIPAddrString(int ipa)
{
   StringBuilder b = new StringBuilder();
   b.append(Integer.toString(0x000000ff & (ipa >> 24)));
   b.append(".");
   b.append(Integer.toString(0x000000ff & (ipa >> 16)));
   b.append(".");
   b.append(Integer.toString(0x000000ff & (ipa >> 8)));
   b.append(".");
   b.append(Integer.toString(0x000000ff & (ipa)));
   return b.toString();
}

I have that first set of code in the try/catch above in a method called dump() in class called IPConfig. Then I just put a main method in IPConfig to call new IPConfig().dump() so that when I'm trying to figure out some wacky network problem, I can see Java thinks is going on. I figured out that my Fedora box reports different information than Windows for the LocalHost information and it was causing my Java programs some issues.

I realize its similiar to the other answers but it prints out nearly everything interesting that you can get from the interface and ipaddress apis.

Tacklind answered 30/1, 2009 at 13:51 Comment(4)

I've got very similar code in the startup procedure for my application. For some reason, RedHat and related linuxes really like to misconfigure the loopback address - I've had inumerable problems caused by 127.0.0.1 being mapped to the hostname rather than localhost on Redhat boxes. – Osithe 30/1, 2009 at 15:25

That's exactly what kept getting me down too. I ended up putting in code that chooses the first non-localhost interface with an IPv4 address and asking that for the hostname, or allowing the user to set a system property that picks the interface by name and set java.net.preferIPv4 – Tacklind 30/1, 2009 at 15:34

It didn't solve the hostname problem necessarily, but it meant that I didn't have to depend on the hostname anymore. – Tacklind 30/1, 2009 at 15:35

InterfaceAddress.getBroadcast() may return null. – Longevous 3/5, 2011 at 9:46

Update to fix Jared's answer for JDK 1.7.

// Get list of IP addresses from all local network interfaces. (JDK1.7)
// -----------------------------------------------------------
public List<InetAddress> getListOfIPsFromNIs(){
    List<InetAddress> addrList           = new ArrayList<InetAddress>();
    Enumeration<NetworkInterface> enumNI = NetworkInterface.getNetworkInterfaces();
    while ( enumNI.hasMoreElements() ){
        NetworkInterface ifc             = enumNI.nextElement();
        if( ifc.isUp() ){
            Enumeration<InetAddress> enumAdds     = ifc.getInetAddresses();
            while ( enumAdds.hasMoreElements() ){
                InetAddress addr                  = enumAdds.nextElement();
                addrList.add(addr);
                System.out.println(addr.getHostAddress());   //<---print IP
            }
        }
    }
    return addrList;
}

As highlighted by Sam Skuce comment:

This doesn't compile in JDK 1.7. getNetworkInterfaces returns an Enumeration which does not implement Iterable. – Sam Skuce Jul 11 '12 at 19:58

Output Example:

fe80:0:0:0:800:aaaa:aaaa:0%8
192.168.56.1
fe80:0:0:0:227:aaa:aaaa:6b5%2
123.123.123.123
0:0:0:0:0:0:0:1%1
127.0.0.1

Otiliaotina answered 26/3, 2013 at 15:28 Comment(0)

import java.net.*;
import java.util.*;

public class NIC {

public static void main(String args[]) throws Exception {

    List<InetAddress> addrList = new ArrayList<InetAddress>();
    Enumeration<NetworkInterface> interfaces = null;
    try {
        interfaces = NetworkInterface.getNetworkInterfaces();
    } catch (SocketException e) {
        e.printStackTrace();
    }

    InetAddress localhost = null;

    try {
        localhost = InetAddress.getByName("127.0.0.1");
    } catch (UnknownHostException e) {
        e.printStackTrace();
    }

    while (interfaces.hasMoreElements()) {
        NetworkInterface ifc = interfaces.nextElement();
        Enumeration<InetAddress> addressesOfAnInterface = ifc.getInetAddresses();

        while (addressesOfAnInterface.hasMoreElements()) {
            InetAddress address = addressesOfAnInterface.nextElement();

            if (!address.equals(localhost) && !address.toString().contains(":")) {
                addrList.add(address);
                System.out.println("FOUND ADDRESS ON NIC: " + address.getHostAddress());
            }
        }
    }

}
}

Breana answered 14/4, 2011 at 9:3 Comment(0)

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Update to fix Jared's answer for JDK 1.7.

Output Example:

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